The following correction was printed in the Guardian's Corrections and clarifications column, Thursday October 26 2006

In the report below, we said that Sir Robin Knox-Johnston was the first person to sail round the world single-handed. We should have included "non-stop"in that description.

For a while it looked like sailing legend Sir Robin Knox-Johnston had been one of the lucky ones. Barely 24 hours into the voyage that marked the 67-year-old's return to solo round-the-world yacht racing, gusts of more than 80mph and waves as high as a house had wreaked havoc in the Bay of Biscay, leaving three of the six yachts which left northern Spain so badly damaged they had to limp back to port.

The last despatch race headquarters had received from Sir Robin, the first person to sail around the world non-stop single handed, was more sanguine: "Wind 58 knots, storm jib up, sea white with spray, surviving not racing, but OK. Irish coffee."

But yesterday it emerged he and his appropriately-named craft, Saga Insurance, had endured the toughest ordeal of all. The vessel had partially capsized, the mast burying itself in the crashing waves. It was so badly damaged that the mainsail could not be raised. He had no choice but to head for dry land.

"Rolled last night," he said in his message to race headquarters. "Section of mast track bent. Cant remove all the screws so sail stuck. Heading Corunna [La Coruña in northern Spain] but may take a day or two. Masthead instruments unserviceable but alarms keep going off. SatC still bleeping. Otherwise OK. RKJ."

A later, more detailed message, said: "Last night was a bad one, one gust reached 72 knots. The waves were huge and the sea white with spindrift. There was an enormous lurch at about 0120 and the boat was knocked on her side by a wave."

Yesterday the organisers of the Velux Five Oceans Challenge defended their decision to go ahead with the start on Sunday when they knew a storm was brewing. The six-month race left Bilbao in northern Spain heading for Fremantle in western Australia, the first of two stop-overs, six weeks and 12,000 miles away.

David Adams, race director, said: "The main problem is that you can't slow these formula one boats down and they simply crash on through - it is bone breaking.

"We always knew that this would be a nasty corner to negotiate. We were expecting strong winds of 40 knots, but none of the weather models or advisers predicted 60 knots. With such conditions, you can expect waves of 12-14 metres.

"I spoke to each of the teams and their weather advisers before they left Bilbao and none of the skippers had concerns about leaving on Sunday."

But they were not long out of port when the storm started to bite. Alex Thomson, another Briton, had taken an early lead but was soon in trouble after becoming snagged on a discarded fishing net and suffering a broken winch. As the wind continued to stiffen one of the sails of his boat, Hugo Boss, was shredded.

Back in Gujon in northern Spain, overseeing repairs, he said: "On a scale of one to 10, it was an 11. It was horrific."

The race's final Briton, Mike Golding, a former firefighter from Southampton, described the seas as "pretty friggin' enormous". He was forced to climb up the mast of his yacht, Ecover, to make running repairs but had to turn back with problems including a holed mainsail.

Sir Robin, who has taken on the challenge to help him recover from the death of his wife Suzanne from cancer in 2003, will arrive in La Coruña tomorrow at the earliest. He is determined to rejoin the race as soon as the repairs are carried out. In a message yesterday he estimated it would take a day to fix the boat "then I'll carry on and try to catch the others up."

He added: "I've been sat in the cockpit watching the waves breaking around the boat. Everything around me is white, you dare not look into it as you would be blinded. It is as bad as anything you would see in the Southern Ocean. I mean, 72 knots, you are up at hurricane level. The boat is otherwise fine and just needs the chance to show herself, she has been riding the waves beautifully - an absolute dream. She's really good, it is just a bit uncomfortable for the human inside her."

100 days of hazard

Racing a yacht around the world single-handed is often described as the maritime equivalent of climbing Everest but there is a good argument that it is even tougher. An estimated 15,000 people have scaled Everest; only 163 have sailed solo around the world.

This year's race has been made even tougher with only two stop-overs in Australia and the US rather than three or four. Sixty foot yachts (18m) are normally raced by a crew of 10-15 - for one person it is an enormous challenge, sailing, navigating, repairing - and finding time to look after themselves.

They face sweltering heat as they cross the Equator and freezing cold in the Southern Ocean and the constant threatof icebergs and submerged objects or of being swept overboard.

When all is going well a skipper might get six hours of sleep a day; if not, it may just be two hours or no sleep at all. Some suffer hallucinations such as believing other crew members are on board. The hazards are ever-present for the estimated 100 days they are actually at sea - and the idea is not just to survive but to win the race.